(a) Field of the Invention:
This invention relates to an illuminating optical system for endoscopes wherein a uniform illumination is obtained with a simple structure.
(b) Description of the Prior Art:
There is already known such illuminating optical systems of this kind as, for example, by Japanese Patent Preliminary Publication No. Sho 58-87523. This shall be explained with reference to FIG. 1. The reference numeral 1 represents an endoscope body including an observing optical system consisting of an objective 2, image guide 3 and eyepiece 4 and an illuminating system consisting of an illuminating lens 5, light guide 6, light collecting lens 7 and light source 8 and further provided with an image receiving device 11 on which an image to be observed is formed by a half prism 9 and lens 10 arranged between the image guide 3 and eyepiece 4, a detecting circuit 12 detecting the brightness distribution in the observing visual field on the basis of a signal from the image receiving device 11 and a driving circuit 13 for moving the light collecting lens 7 in a direction vertical to the optical axis with a signal from the detecting circuit 12. According to this formation, in case the detecting circuit 12 detects an uneven brightness distribution in the observing visual field, the driving circuit 13 will be controlled to drive the light collecting lens 7, and thus the position of the light collecting point by the light collecting lens 7 of the light having come out of the light source 8 will move on the entrance end face of the light guide so that the light distribution characteristic on the object S to be observed will vary and an even uniform illumination will be obtained. However, the illuminating optical system of this type has the disadvantages that a driving mechanism driving the lens to vary the light distribution characteristic is required and that the mechanical structure is complicated.